Disable docker-ce yum repo by default / cleanups (#7080)

Upgrading docker / containerd without adapting the configuration might break the node,
so disable docker-ce repo by default.
We are already using dpkg hold for Debian.

All containerd.io packages provide /usr/bin/runc, so no need to check

yum_conf was never used for containerd

module_hotfixes should not be needed with the EL8 repo

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>